The invention is directed to a locking device for a bobbin that is located in a holding space in the hook base for the bobbin for retaining the bobbin in the hook base.
The bobbin of sewing machines, especially household sewing machines, either can be stored directly in the hook base and is thus directly accessible or it can be inserted into a bobbin case, which is designed specifically for this purpose and which is stored on its side in the hook base. The present invention relates to a bobbin stored directly in the hook base. However, it can also be used for a bobbin stored indirectly in a bobbin case.
From DE-A1 3819405, a bobbin case for rotary hooks is known, in which the bobbin is pushed onto a cylindrical bobbin rod, which is part of the bobbin case, and is held by a securing lever. The securing lever, provided as a two-arm lever, is held by a spring-loaded plate in two positions (open position and working position). The lock is released by manually pivoting the lever by 90° into an axis-parallel position. Then the bobbin can be lifted out of the hook base. To simplify the lifting of the bobbin from the hook base, it is proposed in DE-A1 1951038 to insert a helical spring between the bobbin bottom side, i.e., the underlying bobbin flange, and the hook base. After the lever releases the bobbin, this spring pushes the bobbin partially out of the hook base. At the same time, during sewing, the spring exerts a braking moment on the bobbin and this moment has an effect that is dependent on the top surface of the bobbin and cannot be influenced. This can impair the sewing process.
From GB-A 2149433, a bobbin holder is further known, in which the bobbin is held by a spring-loaded holding rod that can be moved through the bobbin. The holding rod can be brought from the holding position into the removal position by a quarter turn and can be removed together with the bobbin completely from the hook base. Consequently, when a full bobbin is inserted, the holding rod must be inserted into the bobbin and then secured.